In a thin film transistor liquid crystal display (TFT-LCD), the yield of the production process of the TFT which is a core part of the display, directly decides the cost and reliability of the TFT-LCD. For current production processes of the LCD, the preparations of the respective film layers of the TFT are key steps. The size of the gradient at the edge of a thin film layer directly affects the performance of the coverage of the thin film layer deposited in the next step, when the gradient at the edge of a thin film is too steep or perpendicular, this will usually lead to the coverage defect or breakage of the thin film layer deposited in the next step; if the gradient at the edge of the thin film is gentle, the situations of coverage defect or breakage can be avoided to a large extent, thus the control over the gradient at the edge of the thin film layer is a key step in the TFT process.
In current TFT-LCD processes, identical process parameters are used for the production of each film layer, thus the crystallinity and density of each thin film layer are consistent, as illustrated in FIG. 1, the thin film layer 2 is produced on the substrate 3, and the crystallinity and the density of the formed thin film layer 2 are uniform and consistent, when coated photoresist 1 is exposed, during etching, the etching speeds of identical acid concentration (wet etching) or plasma strength (dry etching) to the thin film layer 2 will also be substantially identical, and the effect after the etching is illustrated in FIG. 2, and the gradient at the edge of the thin film layer 2 is relatively steep, which does not help the deposition of the thin film layer 4 in the next process and easily leads to step coverage defect or even breakage, as illustrated in FIG. 3.